Re: [v4 1/4] arm64: kvm: add a cpu tear-down function

AKASHI Takahiro
2015-05-27T05:22:14Z

Marc,

Thank you for your reviews:

On 05/26/2015 06:26 PM, Marc Zyngier wrote:
> Hi Takahiro,
>
> On 08/05/15 02:18, AKASHI Takahiro wrote:
>> Cpu must be put back into its initial state, at least, in the
>> following cases in order to shutdown the system and/or re-initialize cpus
>> later on:
>> 1) kexec/kdump
>> 2) cpu hotplug (offline)
>> 3) removing kvm as a module
>>
>> To address those issues in later patches, this patch adds a tear-down
>> function, kvm_cpu_reset(), that disables D-cache & MMU and restore a vector
>> table to the initial stub at EL2.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> ---
>> arch/arm/kvm/arm.c | 15 +++++++++++++++
>> arch/arm/kvm/mmu.c | 5 +++++
>> arch/arm64/include/asm/kvm_asm.h | 1 +
>> arch/arm64/include/asm/kvm_host.h | 11 +++++++++++
>> arch/arm64/include/asm/kvm_mmu.h | 7 +++++++
>> arch/arm64/include/asm/virt.h | 11 +++++++++++
>> arch/arm64/kvm/hyp-init.S | 32 ++++++++++++++++++++++++++++++++
>> arch/arm64/kvm/hyp.S | 16 +++++++++++++---
>> 8 files changed, 95 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 07e7eb1..251ab9e 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -897,6 +897,21 @@ static void cpu_init_hyp_mode(void *dummy)
>> __cpu_init_hyp_mode(boot_pgd_ptr, pgd_ptr, hyp_stack_ptr, vector_ptr);
>> }
>>
>> +static void kvm_cpu_reset(void *dummy)
>
> It looks like you can entirely loose the "dummy" parameter. The only
> reason some function have this is when they are used from an IPI call.

OK. I will remove all of them.

>> +{
>> + phys_addr_t boot_pgd_ptr;
>> + phys_addr_t phys_idmap_start;
>> +
>> + if (__hyp_get_vectors() == hyp_default_vectors)
>> + return;
>> +
>> + boot_pgd_ptr = kvm_mmu_get_boot_httbr();
>> + phys_idmap_start = kvm_get_idmap_start();
>> + __cpu_reset_hyp_mode(boot_pgd_ptr, phys_idmap_start,
>> + hyp_default_vectors,
>> + kvm_virt_to_trampoline(__kvm_hyp_reset));
>> +}
>> +
>> static int hyp_init_cpu_notify(struct notifier_block *self,
>> unsigned long action, void *cpu)
>> {
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 3e6859b..3631a37 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -1490,6 +1490,11 @@ phys_addr_t kvm_get_idmap_vector(void)
>> return hyp_idmap_vector;
>> }
>>
>> +phys_addr_t kvm_get_idmap_start(void)
>> +{
>> + return hyp_idmap_start;
>> +}
>> +
>> int kvm_mmu_init(void)
>> {
>> int err;
>> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
>> index 4f7310f..f1c16e2 100644
>> --- a/arch/arm64/include/asm/kvm_asm.h
>> +++ b/arch/arm64/include/asm/kvm_asm.h
>> @@ -118,6 +118,7 @@ struct kvm_vcpu;
>>
>> extern char __kvm_hyp_init[];
>> extern char __kvm_hyp_init_end[];
>> +extern char __kvm_hyp_reset[];
>>
>> extern char __kvm_hyp_vector[];
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 8ac3c70..6a8da9c 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -199,6 +199,8 @@ struct kvm_vcpu *kvm_arm_get_running_vcpu(void);
>> struct kvm_vcpu * __percpu *kvm_get_running_vcpus(void);
>>
>> u64 kvm_call_hyp(void *hypfn, ...);
>> +void kvm_call_reset(phys_addr_t boot_pgd_ptr, phys_addr_t phys_idmap_start,
>> + unsigned long stub_vector_ptr, unsigned long reset_func);
>> void force_vm_exit(const cpumask_t *mask);
>> void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>>
>> @@ -223,6 +225,15 @@ static inline void __cpu_init_hyp_mode(phys_addr_t boot_pgd_ptr,
>> hyp_stack_ptr, vector_ptr);
>> }
>>
>> +static inline void __cpu_reset_hyp_mode(phys_addr_t boot_pgd_ptr,
>> + phys_addr_t phys_idmap_start,
>> + unsigned long stub_vector_ptr,
>> + unsigned long reset_func)
>> +{
>> + kvm_call_reset(boot_pgd_ptr, phys_idmap_start, stub_vector_ptr,
>> + reset_func);
>> +}
>> +
>> struct vgic_sr_vectors {
>> void *save_vgic;
>> void *restore_vgic;
>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>> index 6458b53..facfd6d 100644
>> --- a/arch/arm64/include/asm/kvm_mmu.h
>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>> @@ -96,6 +96,7 @@ void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
>> phys_addr_t kvm_mmu_get_httbr(void);
>> phys_addr_t kvm_mmu_get_boot_httbr(void);
>> phys_addr_t kvm_get_idmap_vector(void);
>> +phys_addr_t kvm_get_idmap_start(void);
>> int kvm_mmu_init(void);
>> void kvm_clear_hyp_idmap(void);
>>
>> @@ -305,5 +306,11 @@ static inline void __kvm_flush_dcache_pud(pud_t pud)
>> void kvm_set_way_flush(struct kvm_vcpu *vcpu);
>> void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled);
>>
>> +extern char __hyp_idmap_text_start[];
>
> If you're defining it here, then it worth considering removing the
> similar declaration from mmu.c.

Yes. I will remove them from mmu.c.

>> +#define kvm_virt_to_trampoline(x) \
>> + (TRAMPOLINE_VA \
>> + + ((unsigned long)(x) \
>> + - ((unsigned long)__hyp_idmap_text_start & PAGE_MASK)))
>> +
>> #endif /* __ASSEMBLY__ */
>> #endif /* __ARM64_KVM_MMU_H__ */
>> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
>> index 3070096..7fcd087 100644
>> --- a/arch/arm64/include/asm/virt.h
>> +++ b/arch/arm64/include/asm/virt.h
>> @@ -61,6 +61,17 @@
>> #define BOOT_CPU_MODE_EL1 (0xe11)
>> #define BOOT_CPU_MODE_EL2 (0xe12)
>>
>> +/*
>> + * HVC_RESET - Reset cpu in EL2 to initial state.
>> + *
>> + * @x0: entry address in trampoline code in va
>> + * @x1: identical mapping page table in pa
>> + * @x2: start address of identical mapping in pa
>> + * @x3: initial stub vector in pa
>> + */
>> +
>> +#define HVC_RESET 5
>> +
>> #ifndef __ASSEMBLY__
>>
>> /*
>> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
>> index c319116..2614cfc 100644
>> --- a/arch/arm64/kvm/hyp-init.S
>> +++ b/arch/arm64/kvm/hyp-init.S
>> @@ -115,6 +115,38 @@ target: /* We're now in the trampoline code, switch page tables */
>> eret
>> ENDPROC(__kvm_hyp_init)
>>
>> + /*
>> + * x0: HYP boot pgd
>> + * x1: HYP phys_idmap_start
>> + * x2: HYP stub vectors
>> + */
>> +ENTRY(__kvm_hyp_reset)
>> + /* We're in trampoline code in VA, switch back to boot page tables */
>> + msr ttbr0_el2, x0
>> + isb
>> +
>> + /* Invalidate the old TLBs */
>> + tlbi alle2
>> + dsb sy
>> +
>> + /* Branch into PA space */
>> + adr x0, 1f
>> + bfi x1, x0, #0, #PAGE_SHIFT
>> + br x1
>> +
>> + /* We're now in idmap, disable MMU */
>> +1: mrs x0, sctlr_el2
>> + ldr x1, =SCTLR_EL2_FLAGS
>> + bic x0, x0, x1 // Clear SCTL_M and etc
>> + msr sctlr_el2, x0
>> + isb
>> +
>> + /* Install stub vectors */
>> + msr vbar_el2, x2
>
> Instead of using a parameter, can't you just do
>
> adr x2, __hyp_stub_vectors
> msr vbar_el2, x2
>
> ? I can't imagine a case where we don't want this behaviour, and this
> would slightly simplify the calling convention.

Yeah, but it will also enforces kvm to be statically linked to the kernel.
(not module-capable) Is that OK?

>> +
>> + eret
>> +ENDPROC(__kvm_hyp_reset)
>> +
>> .ltorg
>>
>> .popsection
>> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
>> index fd085ec..7c3bdee 100644
>> --- a/arch/arm64/kvm/hyp.S
>> +++ b/arch/arm64/kvm/hyp.S
>> @@ -1136,6 +1136,11 @@ ENTRY(kvm_call_hyp)
>> ret
>> ENDPROC(kvm_call_hyp)
>>
>> +ENTRY(kvm_call_reset)
>> + hvc #HVC_RESET
>> + ret
>> +ENDPROC(kvm_call_reset)
>> +
>> .macro invalid_vector label, target
>> .align 2
>> \label:
>> @@ -1179,10 +1184,14 @@ el1_sync: // Guest trapped into EL2
>> cmp x18, #HVC_GET_VECTORS
>> b.ne 1f
>> mrs x0, vbar_el2
>> - b 2f
>> + b 3f
>
> How about renaming this to something like "do_eret" once and for all so
> that we stop this dance each time someone adds a new entry point?

Good point. I will take it.

>> -1: /* Default to HVC_CALL_HYP. */
>> + /* jump into trampoline code */
>> +1: cmp x18, #HVC_RESET
>> + b.ne 2f
>> + br x3 // no return
>
> Same here. If we're always jumping to the trampoline code, why do we
> have to pass it as a parameter?

We need here a physical address of reset function. It seems easy to call
kvm_virt_to_trampoline() in C code. But, yes, we can also do it in asm.

Thanks,
-Takahiro AKASHI

>>
>> +2: /* Default to HVC_CALL_HYP. */
>> push lr, xzr
>>
>> /*
>> @@ -1196,7 +1205,8 @@ el1_sync: // Guest trapped into EL2
>> blr lr
>>
>> pop lr, xzr
>> -2: eret
>> +
>> +3: eret
>>
>> el1_trap:
>> /*
>>
>
> Thanks,
>
> M.
>